The best method of knowing how much fertilizer to apply is by taking a soil test. You can go through Utah State University Extension if you like, and forms are available online through the USU Analytical Lab (www.usual.usu.edu/) or at our local office located at 125 West 200 South.
However, not everyone has time or wants to take a soil test, so for those people, here is some general information about fertilizing fruit trees.
First, the most common time to fertilize fruit trees is between spring and early summer. Next, it’s good to understand what each of the three main plant nutrients assists plants in accomplishing. Nitrogen provides nutrients for growth, leaf development and color and improved fruit production. Phosphorus, along with nitrogen, helps with photosynthesis, plant growth, blooming and root growth. Potassium also helps with photosynthesis as well as improved fruit quality and resistance to diseases.
For those who have been using a complete fertilizer on their trees and landscapes, meaning one with the three main nutrients discussed above, it’s very possible that your soil has more than enough phosphorus and potassium, unless you are picking heavy fruit loads off each year. It’s likely you don’t need yearly applications of phosphorus or potassium and another value of doing a soil test is that you would know for sure. Nitrogen though, being water soluble, is usually required each year.
Assuming you don’t have a commercial orchard but just a regular landscape with some fruit trees and other plants, one general method of fertilization is to add 1/10 of a pound of actual nitrogen, not just 1/10 of a pound of the product, per inch of trunk diameter. For fruit trees this measurement is often taken one foot off the ground. So if the diameter of your fruit tree was 3 inches that would be 3/10 of a pound of actual nitrogen for that fruit tree; if the tree diameter is 5 inches then 5/10 or 1/2 of a pound of actual nitrogen.
If you are applying a complete fertilizer you should base the amount you apply on the nitrogen component if you haven’t done a soil test. Don’t apply this fertilizer in a band around the tree, but rather broadcast or evenly spread the fertilizer starting about 18 inches away from the tree trunk out to the drip line. If possible, you could scratch the fertilizer into the soil before your next irrigation.
Another method to determine the need to add fertilizer is to look at the annual terminal growth of your fruit tree branches. By this I mean, how much did that branch grow last year. According to the Yellow Jacket Research Center outside of Dove Creek, Colorado, you should be looking at obtaining 24 to 36 inches of terminal growth each season for apple trees that didn’t bear fruit the previous year, for pear trees, look for 12 to 26 inches of growth, and for peach trees, look for 16 to 24 inches of terminal growth. For trees that did bear fruit the terminal growth would be expected to be less. For apple trees that did not bear fruit last year, look for 12 to 14 inches of growth, for pear trees, look for 6 to 12 inches and for peach trees, look for 10 to 15 inches of terminal growth. If you aren’t reaching that amount of terminal growth you might want to up your fertilization a bit. If you are above those levels you can reduce your fertilization.
Thought for the day: “Someone once threw me a small, brown, hairy kiwi fruit, and I threw a wastebasket over it until it was dead.” —Erma Bombeck
Previous articles are available at The Times-Independent website, www.moabtimes.com. Have an idea you’d like Mike to consider writing about? Want more information about these topics? Call the Utah State University Extension Grand County office at 435-259-7558 or email Mike Johnson at firstname.lastname@example.org.